–When did the concert_____?---Oh, two days ago.
When we visited Zhou Zhuang again ten years later, we found it changed so much that we could hardly ________ it.
While________ along the road, Mr. Smith met an old friend of his.
It was with the help of the local guide________ the mountain climber was rescued.
Either you or one of your students________ to attend the meeting that is due tomorrow.
Only when he apologizes for his rudeness________ to him again.